Hepatitis C virus (HCV) is a member of the Flaviviridae family of enveloped, positive-strand RNA viruses and constitutes the type member of the genus Hepacivirus. HCV contains a 5′ uncapped positive strand RNA genome of 9.4 kb, that possesses two overlapping open reading frames: one is translated into a single polyprotein of 3010 amino acids, while the other yields a 17 kDa protein. The viral polyprotein is processed to generate at least 10 different structural and nonstructural proteins. The genome of HCV is highly heterogeneous and the virus circulates as quasispecies in a single infected individual. HCV is primarily hepatotropic, but it has also been implicated in lymphoproliferative diseases such as mixed cryoglobulinaemia, B-cell non-Hodgkin's lymphoma, and Sjögren's syndrome.
HCV is a significant pathogen, with nearly 3% of the world's population, roughly 170 million people, persistently infected. HCV is a significant etiologic agent of chronic liver disease. About 85% of primary infections become chronic, and ˜20% of patients with chronic HCV develop serious complications, such as liver cirrhosis, end-stage liver disease, hepatocellular carcinoma, and death due to liver failure.
The search for HCV drugs as well as for the development of an HCV vaccine is severely hampered by the lack of an efficient tissue culture, or robust cellular system that would support virus replication, or a simple animal system for the study of replication and HCV pathogenicity. The only animal models currently available for the study of this virus are the chimpanzee and a mouse that possesses a chimeric human liver.
Some vitro culture systems attempted for the study of HCV used human cells of hepatocytic and lymphocytic origin, but low and variable levels of replication and virus-induced cytotoxicity posed important problems. Primary hepatocytes (derived from a human donor) can be infected with HCV isolated from serum of infected patients, and the virus can be detected in the supernatant for several weeks after infection, however, the availability of primary hepatocytes is limited and, their isolation is time-consuming and labor-intensive. Consequently, such tissue culture systems are generally considered unsuitable for intensive large-scale antiviral studies.
Another example of a culture system is human hepatoma cells transfected with a vector comprising subgenomic selective replicons cloned from a full-length HCV consensus genome from an infected liver. The proposed system was limited, however, by the fact that only non-structural viral proteins were expressed.
There thus remains a need to provide a culture system that would enable the study of HCV replication and/or pathogenesis and the development of a treatment or prophylaxis for HCV infections.